The projects proposed in this Program Project Grant (PPG) are complex both physiologically and technically. In order to allow the individual investigators to concentrate on the science that is the central part of their projects, we propose to establish a core facility to provide technical support as needed for the successful completion of the specific aims of each individual groups. The group of people that will comprise the Instrumentation and Software Core are already central contributors to the laboratory with substantial experience in supporting the proposed project. The mission of the Instrumentation and Software Core is to provide hardware and software and development to the projects and core laboratories of this PPG. The core will be available to the electrical and optical mapping projects and the numerical modeling studies, as well as the other core laboratories. The specific responsibilities of the core will be as follows: 1. Support and develop application software as needed by PPG investigators. 2. Support and develop optical and electrical mapping systems. 3. Administer the local area network for the PPG projects. 4. Provide electrodes for electrical mapping studies in the PPG. 5. Extend the existing telemetry system to new sensors and capabilities. 6. Satisfy general instrumentation needs, including special purpose stimulators, defibrillators, and data acquisition system.